This invention relates to logic control systems and more specifically it relates to fluid logic elements of the taut diaphragm type provided with electrical switching contacts indicating the various logic conditions signified by displacement of the diaphragm.
Diaphragm type fluid logic devices for operation with on-off type digital fluid flow signals are well known in the art. Thus, flip-flop functions are attained as shown for example in Ser. No. 349,635 filed by the common assignee of this invention for Fluid Operated System, now U.S. Pat. No. 3,789,864. Another example is the logic OR device described in Ser. No. 165,446, Fluid Operated Logic Device, now U.S. Pat. No. 3,779,267.
While logic systems incorporating such fluid logic elements are advantageous since they are compact, efficient, inexpensive and operate quickly over a long reliable lifetime, there are some problems presented in fluid systems. One such problem is the R-C time constant effect of fluid flow passage through a long fluid flow channel. This might cause errors in response or timing of some logic elements, and may limit the fluid logic systems to those applications which may be confined within reasonable boundaries of location. Such is not so with electric wires.
Another problem encountered is the interfacing of the fluid applications with electrical systems or load devices such as relays, which otherwise might be used advantageously to improve system performance and flexibility. A simple spring switch assembly might be actuated by flexing a diaphragm to operate the spring in a conventional manner, but this not only is unwieldy and expensive but also interferes with the timing and loading characteristics of the logic element and thus may be incompatible with the system requirements. More important is the fact that this is an indirect indication of fluid conditions which may not exactly follow the behavioral response of the logic element, it diaphragm or the fluid paths controlled thereby.
Another not trivial set of problems is in the cost of electric switch interfacing and mechanical compatibility of switching structure with the fluid logic elements. Thus, for example, the logic elements may require special mounts or structures to accommodate the switches which would be difficult to locate in situ on a machine location or in a compact modular assembly of logic elements.
Further the servicing of fluid logic systems has been difficult, particularly in integrated or modularized complex systems, where it is difficult to isolate operating conditions of individual elements or circuit sections. Some kinds of problems may be sensed by pressure gages at key system junctures to show general operation conditions. However in a complex system, it may become important to isolate problems to a specific element or portion thereof so that an extra unit might be substituted for a defective one without requiring extensive system access. For example the proper seating of a diaphragm on a nozzle is required to seal a flow path. If the path is not sealed the condition may be shown by a pressure gage. However, the position of the diaphragm is not known so the condition causing the lack of sealing may not be evident and the nature of the problem is not isolated because there are no known simple prior art indicators of the diaphragm position or diaphragm wear and operating conditions in dynamnic conditions encountered with fluid logic elements.
Also the general reliability requirement for redundancy, or the provision of certain types of logic patterns may be complex by use solely of fluid logic. For example a logic "not" function is not readily achieved by simple logic elements. An electric transfer switch, however, simply provides either a logic signal or its inversion. Accordingly, the "logic power" of a system confined to fluid logic alone is generally limited in scope and may result in a system more complex than could be attained by logic elements providing more versatile logic functions.